Castors

ABSTRACT

A support structure for a castor, a castor provided with such a support-structure, and a castored trolley is described. The support structure comprises a first member  5 , a second member  3  that is rotatable with respect to the first member about a pivot axis, and magnetic means  21, 23, 61, 63  that is operable up to a certain torque to restrain movement of the rotatable member from one angular position with respect to the first member. Preferably the magnetic means comprises at least one hair of magnetically co-operable components. Preferably one component of the at least one pair of components is a permanent magnet. In another angular positions without registration of the first and second members free rotation is possible unless and until re-registration occurs.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is the national stage of the InternationalPatent Application No. PCT/GB2003/003700, published in English and filedAug. 26, 2003, which claims the benefit of GB Provisional ApplicationNo. 0219942.0 filed Aug. 28, 2002, and GB Provisional Application No.0303274.5 filed Feb. 12, 2003, all of which are hereby incorporated byreference in their entirety.

The present invention relates to a support structure for a castor, to acastor provided with such a support structure, and to a castoredtrolley, especially a manually movable trolley, such as a supermarkettrolley, a roll container, or a hospital trolley, but without limitationto same.

The majority of such trolleys, intended for the transport of goods orpersons, are normally provided with four castors, each freely rotatablethrough 360°. In practice, this frequently leads to steeringdifficulties, either during required straight line movement, or whennegotiating a corner or bend.

With a view to providing some steering control it is known to restrainthe freedom of rotation of a castor by means of a spring loaded pinengaging in a recess, but such control proposals have been subject tominimal adoption.

An aim of the present invention is the provision of an improved supportstructure for a castor, and consequently an improved castor, and animproved castored trolley.

Accordingly a first aspect of the present invention provides a supportstructure for a castor comprising a first member, a second member thatis rotatable with respect to the first member about a pivot axis, andmagnetic means that is operable up to a certain torque to restrainmovement of the rotatable member from one angular position with respectto the first member.

Conveniently, said one angular position corresponds to a desiredregistration of the first and second members. In other angular positionsthe magnetic means may be operable to permit free rotation unless anduntil re-registration occurs. Additionally or alternatively the magneticmeans may be operable to bias the rotatable member into said one angularposition when displaced therefrom.

The first and second members may comprise first and second plates. Thefirst and second members may be located in co-axial spaced apartrelationship so as to provide mutually facing surfaces. Bearing meansmay be located between the first and second members.

The magnetic means comprises at least one magnet. Preferably themagnetic means comprises at least one permanent magnet. Moreparticularly the magnetic means comprises at least one pair ofmagnetically co-operable components, which may be the aforesaid firstand second members, separate components or at least one separatecomponent. More preferably they are two separate components. Whenseparate components are provided one component of at least one pair ofmagnetically co-operable components is conveniently mounted with respectto each of said first and second members. More particularly a small airgap between the magnetically co-operable components creates a magneticflux that provides said restraining effect.

A specific embodiment of the invention provides a support structure fora castor, comprising:

-   -   (i) first and second plates located in co-axial, spaced apart        relationship so as to provide mutually facing surfaces,    -   (ii) bearing means located between the plates whereby one plate        is rotatable with respect to the other plate, and    -   (iii) one component of at least one pair of co-operable        components being mounted on each plate, at least one of which        pair of components is a permanent magnet adapted, in one angular        position of the rotary plate with respect to the non-rotary        plate, to be brought into registration with a relatively small        air gap between adjacent surfaces of the two co-operable        components to create a magnetic flux that, up to a certain        torque restrains rotation, and in other angular positions        without registration permits free rotation unless and until        re-registration occurs.

When the co-operable components are in register, i.e. aligned oppositeone another, the magnetic flux restrains rotation of the rotatablemember so that, when applied to a castor of, for example, a super markettrolley, directional stability is achieved assisting steering of thetrolley. Also, due to the use of magnetic flux to restrain rotation,there are no contact faces and no parts subject to wear. Clearly, thetorque required to exceed the magnetic flux is a factor of the surfacearea of the magnet(s), and the air gap.

A second aspect of the invention provides a castor suitable for amanually movable trolley and comprising a support structure according tothe first aspect of the invention.

The castor comprises a wheel, roller or other ground engaging rollingelement that is mounted rotatably with respect to a support bracket.Conveniently the support bracket constitutes or forms part of theaforesaid second (rotatable) member. Preferably the support bracket is Ushaped. Most usually bearing means is provided between the first andsecond members. Preferably at least one ball or roller bearing is used.

A third aspect of the invention provides a trolley provided with atleast one, and preferably four, castors in accordance with the secondaspect of the invention.

Most usually the non-rotatable member is attached to a leg of thetrolley by a bolt, the head of which engages an outer surface of therotatable member via a second ball or roller bearing. The trolley may bea super market trolley, a roll container, a patient trolley or any otherwheeled conveyance provided with at least one castor for steeringpurposes. Preferably the trolley is manually movable.

Where provided the aforesaid first and second plates may be circular.Conveniently one of the first and second members, and preferably anupper one of the members, has an annular skirt or rim extendingtherefrom toward the other one of the members. More preferably still theskirt shrouds a part of the other member. The skirt preferably enclosesthe magnetic means.

Where a pair of co-operable components is utilized one component of thepair may be a permanent magnet and the other component of the pair maybe a ferro-magnetic element. Alternatively, both components of the pairmay be permanent magnets. The polarity of the magnets may be such as torely on attraction or repulsion to achieve the desired registration ofthe relatively movable members. The permanent magnets may be discmagnets, bar magnets, ring magnets or any other shape of magnet. Anyferro-magnetic element that is used preferably has a shape that is thesame as or complimentary to the shape of the permanent magnet or magnetsthat are used. The ferro-magnetic element is preferably steel. In oneembodiment discs are used for the magnetically co-operable components.In another embodiment the magnetically co-operable components arearcuate, and extend over a limited area in the form of a predeterminedquadrant, e.g. <90° of each plate, in which case the ferro-magneticelement, e.g. steel, is also arcuate, or the second permanent magnet isalso arcuate.

There may be a plurality of pairs of magnetically co-operablecomponents. Configurations other than pairs may be used. A ring magnetand a disc magnet may be used. The ring magnet may be polarized to haveNorth at one edge and South at a diametrically opposite edge. The discmagnet may be polarized to have North confronting the ring magnet, Thusthe disc magnet will be attracted to South on the ring magnet and thecombination will operate to bias the disc magnet into the desiredangular position. However it is preferred to use two pairs ofmagnetically co-operable components. Preferably they are located 180°apart. The pairs of magnetically co-operable components are disposed tohave confronting faces that are slightly spaced apart to define an airgap therebetween. Preferably means is provided to adjust the spacing.Conveniently at least one component of the or each of the magneticallyco-operable components is secured by screw means that facilitatesadjustment of the axial spacing of the pairs of components. Thisprovides for adjustment of the air gap.

In another embodiment at least one of the magnets may be anelectromagnet and means may be provided to selectively energize andde-energize it.

The various aspect of the present invention will now be describedfurther hereinafter, by way of example only, with reference to theaccompanying drawings; in which:

FIG. 1 is a broken away perspective view of a first embodiment of castorembodying the invention,

FIG. 2 is a view corresponding to FIG. 1 but ghosted in part to showfurther constructional features,

FIG. 3 is an end view of another embodiment of castor embodying theinvention,

FIG. 4 is an underneath plan view of the embodiment of FIG. 3,

FIG. 5 is a section on X-X of FIG. 3,

FIG. 6 is an enlarged sectional view of the part shown circled in FIG.3,

FIG. 7 is a schematic plan view showing the disposition of the magnetsaccording to one embodiment, and

FIG. 8 is a schematic side view of a trolley embodying the invention.

FIGS. 1 and 2 show a castor according to one embodiment that is adaptedfor securing to an item (not illustrated) that is required to beprovided with a castor. The item may be a trolley as illustrated in FIG.8. The castor comprises a wheel 1 mounted rotatably with respect to asupport bracket 3 for rotation about axis Y. The support bracket itselfis adapted to be mounted for rotation about pivot axis X. In theillustrated embodiment a swivel assembly is provided of which a cap 5constitutes a first (non-rotatable) member thereof that in practice issecured fixedly with respect to the item to which the castor is secured,and the support bracket constitutes a second (rotatable) member thereof.The castor is secured in place by a headed fixing bolt 6 whose threadedshank is visible at 7 and whose head engages with the underside ofsecuring washer 9. Support bracket 3 is formed with annular grooves 11,13 to its opposite sides to receive respective sets of balls 15, 17constituting bearing means of the castor assembly. One set of ballsengage with the securing washer 9, whilst the other set engage with theunder side of cap 5. Thus in the installed position the support bracket3 is located rotatably between the cap and the securing washer.

Magnetic means is provided that is operable to influence movement of therotatable part of the castor relative to the non-rotatable part, asdescribed further hereinafter. More particularly at least one pair ofmagnetically co-operable components 21, 23 are provided, one of which 21is mounted fixedly with respect to the first member, i.e. the cap 5, andthe other 23 is mounted fixedly with respect to the second member, i.e.the support bracket 3. More particularly, the cap 5 has an annularrecess 19 that accommodates the magnetically co-operable components 21,23. The magnetically co-operable components can take a number ofdifferent configurations as described elsewhere in this specification.However, irrespective of the particular configuration, the magneticmeans is operable, up to a certain torque, to restrain movement of therotatable member from one angular position with respect to thenon-rotatable member.

Thus the magnetic means relies on the principles of magnetic attractionand/or repulsion according to the configuration of the magneticallyco-operable components.

In the embodiment of FIGS. 1 and 2, components 21 and 23 each comprisetwo pairs of permanent magnets 21 a, 23 a, 21 b, 23 b with each pairpositioned 180° apart. The positioning of the magnets relative to oneanother is such that the respective North and South poles thereof willbe adjacent when the movable part of the castor is in a desired angularposition. The confronting faces of the two magnetically co-operablecomponents are spaced slightly apart to ensure that there is always anair gap between the components and thereby maintain the effect of themagnetic flux therebetween. The components 21 a, 21 b and 23 a, 23 bhave a discrete length that occupies part of an annulus. I.e. they areeach annular segments. In FIG. 2 the components 21 a, 23 a have beenmarked with the letters N and S to show as an example the polarizationof the two components at that point. Thus in the illustrated embodimentthe components are magnetized to have the confronting surfaces ofopposite polarity. Thus the components 21 and 23 will be attracted toone another whenever their magnetic fluxes are sufficiently close tointeract. As soon as they escape the range thereof the rotatablecomponent will be able to move freely. However as soon as the componentsmove within range they will again be attracted to one another. Becauseeach of components 21 and 21 is polarized in the same way, it will beseen that the rotatable member can be restrained in said one angularposition when it is in two alternative positions 180° apart. Where thisis not required, the components 21 a, and 23 a can be polarized in theopposite way to components 21 b and 23 b. Thus when component 23 bapproaches component 21 a there will be repulsion.

As mentioned above, only one of the pairs of components 21 and 23 maybea permanent magnet and the other may be a ferro-magnetic material.

If a turning moment is applied to the movable part of the castorrelative to the non-movable part, the attraction between the North andSouth poles will resist the effect of the turning moment and by thismeans the wheel is restrained from moving away from said one angularposition that corresponds to the registration of the first and secondmembers and in the illustrated embodiment to the registration of themagnetically co-operable components. However steering movements arestill possible because the magnetic flux has a finite value and onceovercome will allow the rotatable member to move from said one angularposition. Thus the rotatable member will be freely movable over therange of angular movement that is free of the influence of themagnetically co-operable components.

Referring now to FIG. 3 to 6. Parts corresponding to those referred toin the embodiment of FIGS. 1 and 2 are identified with the samereference numbers. An end of a trolley leg is shown at 31 and isprovided with mounting block 33 that is threaded to receive acomplimentarily threaded mounting bolt 6 to facilitate fixing of acastor assembly to the end thereof. The castor assembly comprises awheel 1 rotatably mounted with respect to support bracket 3. The wheelis rotatable about axis Y and the mounting bracket is pivotable aboutaxis X. Support bracket 3 has two limbs 35, 37 depending from a bridgingportion 39. The bridging portion is secured by four bolts 41 to a lowermounting plate 43 which in the illustrated embodiment is generallycircular with a co-axial through hole 45 of stepped diameter to secureand locate one half 47 a of a lower thrust bearing 47. The head of bolt6 engages with the other half 47 b and ball bearings 48 are trappedbetween the two halves 47 a, 47 b. An upper mounting plate 49 has adownwardly extending rim 51 and a downwardly extending apertured centralboss 53. A second thrust 53 bearing has its upper half 53 a located onthe underside of the upper mounting plate concentric with the boss 53.The lower half 53 b of bearing 53 engages with a central boss 55 of thelower mounting plate thereby mounting the lower mounting plate rotatablywith respect to the upper mounting plate. The upper and lower mountingplates have annular confronting surfaces 59, 60 axially spaced apart toreceive magnetic means.

In the illustrated embodiment the magnetic means comprise two pairs ofcomponents 61 a, 63 a and 61 b, 63 b. The components comprise respectivemagnetic discs. The two pairs of components are spaced 180° apart. Whenthe two pairs of components are in registration as shown in the drawingthe wheel 1 is restrained in a desired angular position as representedby axis Z. Again, one component of each pair of components may be aferro-magnetic material, such as steel.

The lower of the two components are secured to the lower mounting plateby respective countersunk screws 65. The upper of the two components aresecured to the lower mounting plate by respective countersunk screws 67cooperating with a respective nut 69. The confronting surfaces of themagnetically co-operable components are axially spaced apart to ensurethat an air gap exists therebetween. The screws 65 and/or 67 facilitateadjusting the axial spacing of the components 61 and 63. Shims may beused in setting the desired spacing. The upper and lower plates willusually be of non-ferro-magnetic material, hence the use of magnetsand/or ferro-magnetic material for said magnetically co-operablecomponents.

By polarizing the disc magnets so that the confronting surfaces ofcomponents 61, 63 have opposite polarity, the pairs of components willbe attracted to one another in the same manner as described above. Thusthe rotatable plate will be restrained in the desired angular position,represented by axis Z, relative to the non-rotatable plate and in usewill encourage straight line movement of the item to which such castorsare fitted in the absence of a contrary steering movement.

From the above examples it will be apparent how magnetic attraction isused to promote a desired angular position of the rotatable part withrespect to the non-rotatable part. FIG. 7 illustrates how repulsion canbe used to achieve the same effect. Here three magnetically co-operablecomponents are used. Two magnets 71 are positioned at spaced positionson a common pitch circle diameter and secured with respect to the nonrotatable member, whilst a third magnet 73 is secured with respect tothe rotatable member and positioned to be disposed intermediate themagnets 71. The polarity of the three magnets are configured so that themagnetic flux acts to repel magnet 73 from each of magnets 71 into theposition shown and thereby urge the rotatable member into a desiredangular position with respect to the non rotatable member.

Referring now to FIG. 8 there is illustrated a trolley 81 in the form ofa typical super market trolley having a wire basket 83 carried on aframework 85 and provided with a handle 87 for use in maneuvering thetrolley. The trolley is provided with four castor assemblies 89 (onlytwo of which are visible in the side elevation of FIG. 8) embodying theinvention hereof. The castor assemblies are not described in detail asthey may correspond to any of the embodiments described herein that areoperable as described to constrain the wheels thereof to adoptpreferentially said one angular position. In practice said one angularposition will be such as to predispose the trolley to move in astraight-ahead direction. This may dictate that each of the castors issecured to the framework in such a way that said one angular positionlies in the same plane or at least planes that are parallel. On theother hand the planes may be slightly inclined with respect to oneanother so as to give rise to a self centering steering effect as iscommonly used in motor vehicles. I.e. with the respective wheelsadopting a so-called toe in configuration.

The construction of the magnetically co-operable components described inthe above embodiments may be replaced by any of the alternativeconfigurations mentioned above as will be apparent to one skilled in theart.

1. A support structure for a castor comprising a first member, a secondmember that is rotatable with respect to the first member about a pivotaxis, and magnetic means that is operable up to a certain torque torestrain movement of the second member from one angular position withrespect to the first member, wherein said magnetic means comprises afirst magnet associated with the first member and a second magnetassociated with the second member, said first magnet being coaxiallyaligned with respect to said second magnet wherein said first magnet andsaid second magnet are disposed to have confronting faces that arespaced apart to define an air gap therebetween, and means is provided toadjust the spacing between confronting faces of said first magnet andsaid second magnet.
 2. A support structure for a castor as claimed inclaim 1 in which said one angular position corresponds to a desiredregistration of the first and second members.
 3. A support structure fora castor as claimed in claim 1, in which the magnetic means is operableto bias the second member into said one angular position when displacedtherefrom.
 4. A support structure for a castor as claimed in claim 1, inwhich the first and second members have co-axial spaced apart mutuallyfacing surfaces.
 5. A support structure for a castor as claimed in claim1, in which the magnetic means comprises a plurality of magneticallyco-operable components at least one of which is associated with thefirst member and at least one of which is associated with the secondmember.
 6. A support structure for a castor as claimed in claim 1, inwhich the magnetic means comprises at least one permanent magnet.
 7. Asupport structure for a castor as claimed in claim 1, in which themagnetic means comprises at least one ferro-magnet.
 8. A supportstructure for a castor as claimed in claim 1 in which said air gapbetween said first magnet and said second magnet creates a magnetic fluxthat provides said restraining effect.
 9. A support structure for acastor as claimed in claim 1, in which one of the first and secondmembers has an annular skirt or rim extending therefrom toward the otherone of the members.
 10. A support structure for a castor as claimed inclaim 9 in which the skirt encloses the magnetic means.
 11. A supportstructure for a castor as claimed in claim 1 in which said first magnetis a permanent magnet and said second magnet is a ferro-magneticelement.
 12. A support structure for a castor as claimed in claim 1 inwhich both said first magnet and said second magnet are permanentmagnets.
 13. A support structure for a castor as claimed in claim 1, inwhich a disc is used for said first magnet or said second magnet.
 14. Asupport structure for a castor as claimed in claim 1, in which eitherthe first magnet or the second magnet is arcuate.
 15. A supportstructure for a castor as claimed in claim 1, in which a plurality ofpairs of magnetically co-operable components are used and disposed atspaced positions on a common pitch circle diameter.
 16. A supportstructure for a castor as claimed in claim 15 in which two pairs ofmagnetically co-operable components are used that are located 180°apart.
 17. A castor suitable for a manually movable trolley andcomprising a support structure according to claim
 1. 18. A castor asclaimed in claim 17 and comprising a wheel, roller or other groundengaging rolling element that is mounted rotatably with respect to asupport bracket.
 19. A castor as claimed in claim 17 in which thesupport bracket constitutes or forms part of the aforesaid secondmember.
 20. A trolley provided with at least one castor as claimed inclaim
 17. 21. A trolley as claimed in claim 20 when provided with fourcastors.
 22. A trolley as claimed in claim 20 when manually movable. 23.A support structure for a castor, comprising: (i) first and secondplates located in co-axial, spaced apart relationship so as to providemutually facing surfaces, (ii) bearing means located between the plateswhereby one plate is rotatable with respect to the other plate, and(iii) one component of at least one pair of co-operable components beingmounted on each plate, at least one of which pair of components is apermanent magnet adapted, in one angular position of the rotary platewith respect to the non-rotary plate, to be brought into registrationwith a relatively small air gap between confronting adjacent surfaces ofthe two co-operable components to create a magnetic flux that, up to acertain torque restrains rotation, and in other angular positionswithout registration permits free rotation unless and untilre-registration occurs wherein said components of said at least one pairof co-operable components mounted on each plate are co-axially alignedwith respect to one another and means is provided to adjust the spacingbetween confronting surfaces of said two co-operable components.